I looked at both experiments, and they are very different. The ion engine project is more of a research project, and the fuel cell project requires building a fuel cell from a kit. The fuel cell project will take much longer to complete. I don't think either project will be a "winner' without significant modification by the student (which is a good idea anyway.) Judges don't tend to like either research projects or "kit" projects. Questions to ask yourself:

How much time do you have?How much do you want to spend?Do you prefer virtual projects or "hands-on" projects?How can you extend the project into something more interesting?

How much time do you have? 8 months +-How much do you want to spend? Any Amount of time required to make it a good projectDo you prefer virtual projects or "hands-on" projects? I like both equallyHow can you extend the project into something more interesting? Yes I am considering doing something like this http://www.youtube.com/watch?v=BwqD3uebmy4.